1. Industrial Field of the Invention
The present invention relates to a process for fabricating an insulated gate-structured semiconductor device such as a thin film transistor (TFT) or a thin film diode (TFD), comprising a non-single crystal silicon film formed on an insulating substrate such as a glass substrate or on an insulating film formed on various type of substrate. The present invention also relates to a process for fabricating a thin film integrated circuit (IC) to which TFT or TFD is applied, and more particularly, to a thin film integrated circuit (IC) for an active-matrix type liquid crystal displaying unit.
2. Prior Art
Semiconductor devices developed heretofore comprising TFTs on an insulating substrate (such as a glass substrate) include an active matrix-addressed liquid crystal display device whose pixels are driven by TFTs, an image sensor, or a three-dimensional integrated circuit.
The TFTs utilized in those devices generally employ a thin film non-single crystal silicon semiconductor. The thin film non-single crystal semiconductors can be roughly classified into two; one is a type comprising amorphous silicon semiconductor (a--Si), and the other is a type comprising crystalline silicon semiconductors. Amorphous silicon semiconductors are most prevailing, because they can be fabricated relatively easily by a vapor phase process at a low temperature, and because they can be readily obtained by mass production. The physical properties thereof, such as electric conductivity, however, are still inferior to those of a crystalline silicon semiconductor. Thus, to implement devices operating at an even higher speed, it has been keenly demanded to establish a process for fabricating TFTs comprising crystalline silicon semiconductors. Known crystalline semiconductors suitable for the purpose like this include polycrystalline silicon, microcrystalline silicon, amorphous silicon partly comprising crystalline components, and semiamorphous silicon which exhibits an intermediate state between crystalline silicon and amorphous silicon.
Known process for fabricating crystalline thin film silicon semiconductors includes depositing an amorphous semiconductor film by plasma CVD or low pressure CVD, and applying thereto thermal energy for a long duration of time (i.e., thermal annealing) for crystallization.
In general, silicon semiconductors need to be heated to a temperature of 600.degree. C. or higher. More preferably, heating at 640.degree. C. or higher is necessary to further enhance the crystal growth. However, such a high temperature heating has a problem of thermally influencing the substrate. Furthermore, since the heating time required for crystallization was several tens hours or longer, productivity was low. Therefore, it has been demanded to lower the heating temperature and shorten the heating time.
As a means to overcome the aforementioned problems, a process for crystallizing the film by increasing the surface temperature of the film to substantially 800.degree. C. or higher has been developed. The process comprises irradiating an intense light such as an infrared radiation or a visible light for a duration of about 10 to 1,000 seconds to the surface of the film. This process, which is called as lamp annealing or rapid thermal annealing (RTA), is expected to be process for reducing the influence on substrates, because the duration of heating can be extremely shortened.
However, since the film formed by plasma CVD and low pressure CVD contains a lot of hydrogen combined with silicon, the decomposition reaction of hydrogen is mainly caused by RTA owing to the short time of RTA, that is, the crystallization does not sufficiently proceed. Furthermore, there is a problem that hydrogen is ejected to the exterior of the film by the decomposition reaction of hydrogen to degrade the morphology of the film surface. The present invention has been accomplished in the light of the above circumstances. Accordingly, an object of the present invention is to provide a silicon film suitable for forming a semiconductor device and having a sufficiently high crystallinity.